Fixes#1893Closes#1894
Explain how to get Xcode CLT and gcc via homebrew in installer at the end using a conclusion.html file.
Clarify this also in the manual.
The installation of Homebrew + GCC necessitates Xcode Command Line Tools, which will be installed if it is not present.
The installation of Homebrew + GCC is optional and can be deselected by the user.